Method of dispersing reinforcing pigments in a latex

ABSTRACT

There is disclosed a process for blending rubber latices with carbon black or other reinforcing pigments which comprises the use of a 60/40 to 40/60 butadiene/methacrylic acid latex which has been converted to a water soluble polymer through treatment with an alkali metal hydroxide. Said converted butadiene/methacrylic acid latex is then combined with dry carbon black at a level of 1 to 2 percent butadiene/methacrylic acid dispersing latex solids based on weight of the carbon black. The blended carbon black butadiene/methacrylic acid dispersion is added to rubber latices prior to coagulation. More specifically, this invention is concerned with a carbon black dispersion and its addition to a rubber latex.

TECHNICAL FIELD

This invention relates to a process for blending latex rubber and carbonblack or other reinforcing pigments. The process of the presentinvention provides a rubber latex having uniformly dispersed therein areinforcing agent.

BACKGROUND ART

Carbon black is widely used as a reinforcing agent in rubber.Conventionally, carbon black or like reinforcing pigments, such assilica, have been incorporated into rubbery polymers by vigorous highshear milling in a suitable mixer. However, during commercial mixingoperations of this type the carbon black tends to agglomerate in therubber thereby producing large clumps of pigment and an unsatisfactorydegree of pigment dispersion.

Recently processes of the type wherein the carbon black is dispersed inthe latex form of the rubber have found wide use in the rubber industryand have overcome many of the disadvantages of conventional dry mixing.

U.S. Pat. No. 3,317,458 discloses a process for the production of avulcanizable elastomer wherein carbon black and a light reinforcingfiller, i.e. silicon dioxide, are added to the latex of the elastomer.The carbon black and light filler components are mixed with said latexin the form of an aqueous suspension.

U.S. Pat. No. 3,298,984 is concerned with a method of reinforcing arubber in its latex form which comprises preblending the reinforcingagent with the carrier and then blending the preblend of carrier andreinforcing agent with the rubber latex to thereby produce a reinforcedrubber latex. The carrier or dispersing agent is a water solublephenolic resin, particularly the condensates resulting from the reactionof an aldehyde with a phenol are desirable carriers or dispersing agentsin bringing about the intimate association of the reinforcing agent withthe rubber particles of the latex. Specific carriers or dispersingagents such as the condensates resulting from the reaction offormaldehyde and a polyhydric phenol such as resorcinol are disclosed.

United Kingdom Pat. No. 1,125,801 relates to the production of a carbonblack masterbatch of natural rubber formed by the mixing of carbon blackwith rubber in latex form followed by the simultaneous coagulationtogether of rubber and carbon black. The carbon black is stirred intowater containing a dispersing agent. Dispersing agents, such as thesodium salt of methylene dinaphthalene sulfonic acid sold under thetrademark of "Dispersol LN" and a sodium salt of the sulphonationproduct of lignin which is sold under the Trade Name of Marasperse CBare disclosed.

U.S. Pat. No. 3,021,226 discloses a method for preparing carbon blackslurries using a rosin acid soap as the dispersing agent which comprisesmixing the carbon black with water in the presence of at least 5 partsby weight of a rosin acid soap and at least 0.2 parts by weight of analkali metal or ammonium hydroxide per 100 parts of carbon black.

U.S. Pat. No. 3,023,188 discloses carbon black slurries prepared bydispersing carbon black in alcohol and a minor amount of an alkali metalhydroxide.

U.S. Pat. No. 2,794,749 discloses a method for dispersing furnace carbonblacks in aqueous medium with the aid of a dispersing compositioncomprising a tannic acid product, a lignin material selected from thegroup consisting of lignin and sulfonated derivatives thereof and analkaline material selected from the group consisting of alkali metal andammonium hydroxides.

U.S. Pat. No. 4,098,715 discloses a process for blending liquid rubber,i.e. cements with carbon black. The invention describes a process forblending liquid rubber in carbon black with a high torque mixer. Theliquid rubber (rubber dissolved by an organic solvent) is mixed with arelatively large amount of carbon black to prepare a preliminarydispersion having a relatively high uniformity which is then dilutedwith liquid rubber to give a composition having a desired carbon blackcontent. This is conducted using mixers normally used for viscousliquids such as Banbury mixers or mills.

None of the references describe or suggest the use of a low molecularweight (500-30,000) butadiene/methacrylic acid polymer as a dispersingagent for the incorporation of carbon black in a rubber latex. Theprocess of the present invention provides for blending of latex rubberor rubber in the latex form with carbon black so as to prepare acomposition in which the carbon black is uniformly dispersed in thelatex without the use of high torque mixers. Further, the art does notsuggest the superior dispersions that can be obtained through theprocess of the present invention. High shear mixing of the rubber is notrequired to obtain pigment dispersions and the present process can beused for carbon black, silica pigments and other fillers or pigments. Inaddition, the prior art methods which utilize dispersing agentsgenerally result in a loss in physical properties of the final rubberproduct. The present invention allows for higher solids blackdispersions of excellent stability to be prepared which do not requirehigh shear mixing and do not diminish the final rubber properties.

It is the applicant's unsupported belief that the process of the presentinvention provides excellent final vulcanizate properties due to theability of the butadiene portion of the dispersing polymer to enter intothe curing reaction.

DISCLOSURE OF THE INVENTION

There is disclosed a process for blending latex rubber and a reinforcingagent by stirring and dispersing a mixture of the reinforcing agent inthe rubber latex, the improvement comprising initially contacting thereinforcing agent with a 60/40 to 40/60 butadiene/methacrylic aciddispersing latex which has been converted to a water soluble formthrough treatment with an alkali metal hydroxide at a ratio of dryreinforcing agent to dispersing latex solids in the range of from 90:10to 90:1.

Also disclosed is a method of preparing a reinforcing agent-pigmentrubber latex mixture which comprises initially contacting thereinforcing agent-pigment with a butadiene/methacrylic acid dispersinglatex which has been converted to a water soluble form through treatmentwith an alkali metal hydroxide at a ratio of dry reinforcingagent-pigment to latex solids in the range of from 90:10 to 99:1,thereafter adding the reinforcing agent-pigment butadiene/methacrylicacid mixture to a rubber latex to be reinforced in conventional amountsunder conventional conditions.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, FIG. 1, portrays a graph showing thevariation of absorbance of various samples (A-E) as a function of timeusing a Joyce-Loebl disc centrifuge. The speed at which particles settle(time) is related to particle size and the slope of the curve is relatedto concentration.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present process 90 to 99 parts by weight of reinforcingagent-pigment, i.e. carbon black are mixed with 10 to 1 parts solidsweight of a 60/40 to 40/60 butadiene/methacrylic acid latex which hasbeen converted to the water soluble form through treatment with analkali metal hydroxide. The mixture is stirred to prepare a reinforcingagent-pigment dispersion which is then added to a rubber latex, e.g. astyrene butadiene aqueous polymerization reaction mixture. Thereinforcing agent-pigment/dispersing polymer is then added to a rubberlatex to a predetermined concentration of reinforcing agent-pigmentthereafter the final composition of reinforcing agent-pigment and latexrubber is coagulated to provide a polymer that has uniformly dispersedtherein the reinforcing agent-pigment.

The dispersing latex in the process of the present invention ispreferably a butadiene/methacrylic acid pplymer or resin. This polymerhas a low molecular weight such as from 500 to 30,000. Butadiene is thepreferred conjugated diene monomer in the dispersing latex, however,other monomers such as isoprene, chloroprene, and pentadiene can beused. Carboxylic monomers other than methacrylic acid such as acrylicacid, itaconic acid, fumaric, crotonic and maleic acids can also beused. The conjugated diene/carboxylic monomers are polymerized usingknown emulsion polymerization techniques.

The low molecular weight conjugated diene/carboxylic acid polymer has aterminal functional group as a result of the polymerization and can beeffectively used in the process of the present invention throughtreatment with an alkali metal hydroxide to convert the acid polymer toits water soluble form.

The reinforcing carbon black fillers suitable for use in the presentprocess include those blacks such as: SAF (Super Abrasion FurnaceBlacks), ISAF (Intermediate Super Abrasion Furnace Blacks), HAF (HighAbrasion Furnace Blacks), FEF (Fast Extrusion Furnace Blacks), GPF(General Purpose Furnace Blacks), and FT (Fine Thermal Blacks).

The forms of the carbon black used may vary and include powders,pellets, and soft and hard beads. The process of the present inventionis especially effective when powders are used. Commercial carbon blacksusually contain 0.5 to 2 weight percent water.

The amount of dispersing latex solids (butadiene/methacrylic acid latex)used can vary with the nature of the carbon black but the amount isordinarily from 1 to 10 percent based on the weight of the carbon black,more preferably from 1-3%. The combination of the carbon black with thedispersing latex can be accomplished with any known mixing tecnique.Preferably a high shear mixer is used.

The carbon black with dispersing latex is then added to the rubberlatex. The carbon black/dispersing latex and the rubber latex are thensimultaneously coagulated together to form the reinforced rubber.

The present invention provides a method for reinforcing rubber using aspecialized dispersing latex which permits for the first time the truereinforcement of a rubber in latex form without the necessity ofbreaking down the molecular weight of the rubber on a mill.

The rubber invention preserves the molecular weight of the rubber beingreinforced since the reinforcement thereof occurs in the latex form andthus makes possible for the vulcanization of the reinforced rubber at amolecular weight level that has heretofore been imposible when workingin the dry state. Ordinarily, dry rubber is broken down on a mill toincorporate reinforcing agent from, for example, a molecular weight fromabout 400,000 to about 250,000 (as determined by inherent viscositymeasurements) and is then cured. The 250,000 molecular weight rubberwill have properties inferior to a 400,000 molecular weight rubber curedin the same manner. In the present invention the reinforced rubberrecovered from the latex will have, for example, an undisturbedmolecular weight of 400,000 which can then be cured to produce a rubberhaving properties superior in regard to tensile, elongation, etc. to theproperties of the same rubber if the rubber were broken down on a millduring mixing with carbon black and then cured. It is also believed thatthe dispersing latex of the present invention enters into thevulcanization reaction and thus provides a second reason for thesuperior properties of the instant invention.

An important use for the reinforced latex is in, for example, buildingup a tread for a tire on a pneumatic tire carcass of fabric plies byrotating the fabric carcass in the reinforced rubber latex which hasbeen thickened to the desired degree and then drying each layer of thelatex as it is deposited thereon until the desired thickness of tread isproduced. Another important use of the reinforced latex of thisinvention is in the manufacture of cord rubber adhesives wherein thereinforced rubber latex is compounded with conventional ingredients toproduce an adhesive having exceptional ability to securely bond tirecord to rubber in the construction of a pneumatic tire.

Any rubber initially in a latex form may be reinforced in accordancewith the process of this invention. Such rubbers include natural rubberand any of the known synthetic emulsion rubbers, particularly the dienerubbers and especially the conjugated diene hydrocarbon rubbers that arewell-known in the synthetic rubber art. The process of this invention isalso suitable for the incorporation of reinforcing agent-pigments to asynthetically prepared emulsion of, e.g. butyl rubber or solution SBR.Further, the process of this invention is also suitable for thedispersion of ingredients in plastics, as in the dispersion of carbonblack in toner resin for copiers.

Having generally described this invention a further understanding can beobtained by reference to the examples which are provided herein forpurposes of illustration and are not intended to be limiting unlessotherwise specified.

EXPERIMENTAL

Carbon black slurries were prepared with and without polymericdispersants of the present invention. These slurries were added to anoil extended SBR 1712 rubber latex and the blend was coagulated to givea black masterbatch rubber. The masterbatch samples were compounded intoa conventional tread stock and evaluated with a control compound.

The preferred polymeric dispersants are prepared from butadiene andmethacrylic acid monomers using known emulsion polymerizationtechniques. The latex is diluted to 1 percent solids by weight and thepH is adjusted to 9 to 9.5 with sodium hydroxide. Carbon black slurriesare prepared by grinding the black in water or in water containing thedispersant in a Waring Blender for 5 minutes at high speed.

EXAMPLE 1

The carbon black slurries with or without the present invention wereevaluated for stability using the Joyce-Loebl Disc Centrifuge(hereinafter J/L). Further information of the Joyce-Loebl DiscCentrifuge can be obtained from an article by Provder and Holsworth,Particle Size Distribution Analysis by Disc CentrifugePhotosedimentometry; ACS Organic Coatings & Plastics Chemistry,Preprints, (36) 2, pp. 150-156 (1976). The J/L curve is shown in FIG. 1.Sample A is a normal carbon black/water dispersion. The right side ofthe curve was run at 1500 rpm and the materials which settle out in thisregion are large particles and agglomerates which are unstable. The leftside of the curve represents an 8000 rpm centrifuge speed where all theremaining smaller particles settle out. The speed at which particlessettle (time) is related to the particle size, the slope is related toits concentration. The particles of Sample A settle out almostimmediately at 1500 rpm, therefore, they are all very large andunstable. Sample D (5% by weight budadiene/methacrylic acid dispersantsolids per dry carbon black) is almost a flat line at 1500 rpm so theparticles are all small and the dispersion is quite stable. Sample Erepresents a carbon black sample which has been reduced to its ultimatestructure by ultrasonic dispersion in a Marasperse solution. On acommercial scale, preparation of such an ultimate dispersion is notpractical or economical. Sample E settles at about the same rate asSample D at 1500 rpms. Sample B is the same material as Sample D but thedispersant level is one-half that of D (2.5% of the black content vs5%). Sample C contained 0.01% by weight of a high efficiencyfluorocarbon surfactant. Analysis of numerous carbon black slurriesusing the J/L method revealed that using butadiene/methacrylic aciddispersants with methacrylic acid levels of 60% and 2 parts per hundredof budadiene/methacrylic acid solids per dry carbon black gave the moststable dispersion.

EXAMPLE 2

Carbon black slurries were combined with a laboratory prepared emulsiontype rubber latex and an aromatic extending oil using the techniquesdeveloped for laboratory preparation of oil extended rubber. The threecomponent mixture of carbon black, latex and oil separates withinseconds if the agitation is stopped when prepared in the usual manner.When the polymeric dispersant of the present invention was used at alevel of 2.5% solids on the black, the mixture did not separate forseveral days. Mixtures of latex and black without the oil are morestable but separation occurs within an hour. With the polymericdispersant of the present invention no separation occurs for severaldays. During coagulation the mixtures containing the polymericdispersant of the present invention coagulated as a uniform smallparticle crumb while the customary mixtures produced a black, gray crumbcontaining a considerable amount of free black. After drying there is aconsiderable amount of uncombined carbon black in the customarymasterbatch which rubs off when the sample is touched. The samplecontaining dispersant of the instant invention was clean to the touch;no carbon black rubbed off.

Cure ingredients were milled into all the samples. Compounds were curedand compared to a normal Banbury mixed compound. The results in Table Ishow that there was some loss of carbon black in Sample A, the materialwithout polymeric dispersant, as indicated by specific gravity. Themodulus is low with this sample also. Abrasion results indicate the Picoabrasion is poor for Compound 1 and is slightly improved by the use ofthe dispersant of the present invention; Compound 2.

The present invention allows for solids content of the black slurry tobe raised to 10-15% solids while still maintaining low viscosities. Theuse of the polymeric dispersant of the present invention results inlatex/carbon black/oil mixtures which are stable for several days. Onlya slight separation of oil occurred after 3 days. Mixtures without thedispersant of the present invention separated in several seconds.Coagulated product made with the polymeric dispersant of the presentinvention is more homogeneous than that made without dispersant.Considerable amounts of free black are present when no dispersant isused. Most important of all, the compound properties of the finalproduct are not adversely affected by the dispersant of the presentinvention.

                  TABLE I                                                         ______________________________________                                        TREAD COMPOUNDS                                                                                Compound                                                     Ingredients        1        2                                                 ______________________________________                                        Sample A-Control   206.00   0.0                                               Sample B           0.0      206.00                                            ZnO.sub.2          3.00     3.00                                              Stearic Acid       1.35     1.35                                              Sulfur             1.75     1.75                                              Accelerator        1.40     1.40                                                                 213.50   213.50                                            Rheometer, 300F, 3 Deg. Arc. 100CPM, 60 min. Motor                            Torque, Min.       12.0     14.0                                              Torque, Max.       48.9     54.0                                              TS 2               16.3     13.4                                              T'C90              36.5     33.0                                              T'C95              43.0     40.5                                              Autographic Tensile                                                           Tensile, PSI       3300.    2725.                                             Elongation, %      745.     610.                                              300% Modulus       825.     1050.                                             Hardness, Shore A  61.      66.                                               Best Cure, Min. @ 300 F                                                                          40.      40.                                               Specific Gravity   1.140    1.154                                             Pico Abrasion Index                                                                              86.      94.                                               Mixed              mill     mill                                              Dispersant         no       yes                                               ______________________________________                                    

EXAMPLE 3

Reinforcing agents-pigments other than carbon black are commerciallyavailable and useful in the present invention. Hi Sil 233 (acommercially available reinforcing agent-pigment from PPG Industries)was utilized in place of carbon black. 320 grams of Hi Sil 233 was addedto 1940 grams of water which contained 16 grams of dry solids of a 40:60butadiene/methacrylic acid polymer which was prepared using acceptedemulsion polymerization techniques. The butadiene/methacrylic acidpolymeric dispersant was pre-neutralized to a pH of 10.0 with KOH. Theslurry was agitated at high speeds in a blender for 5 minutes.

The resultant slurry was used to reinforced an SBR 1712 latex. 875 gramsof SBR 1712 latex at 20% solids by weight, 132 grams of aromaticprocessing oil and 1055 grams of the slurry (14.5% solids by weight)prepared above were mixed and then coagulated by pouring into a watersolution containing 3000 ml water, 125 gms. NaCl and H₂ SO₄ to obtain apH of 5-5.5. The reinforced rubber was filtered, washed with cold waterand dried for 5 hours at 90° C. to obtain a powdered, reinforced, rubberproduct.

EXAMPLE 4

Additional experiments were conducted wherein Controls I and II (withoutdispersant of instant invention) were compared with Samples A-D(different levels of dispersant and different methacrylic acid/butadieneratios) of the invention. The procedure as described in Example 2 wasfollowed. Table II lists the components of the controls and the samplesand the physical properties of the resulting rubbers.

                                      TABLE II                                    __________________________________________________________________________    Components     Control                                                                            Control                                                                            Sample                                                                            Sample                                                                            Sample                                                                            Sample                                   Parts by Weight                                                                              I    II   A   B   C   D                                        __________________________________________________________________________    SBR-1712 +     137.50                                                                             --   --  --  --  --                                       37 parts dry carbon                                                           black milled in                                                               SBR-1712 +     --   137.50                                                                             --  --  --  --                                       carbon black/                                                                 water dispersion                                                              SBR-1712 +     --   --   137.50                                                                            --  --  --                                       2.5 parts of 60/40 MA/Bd.                                                     dispersant/carbon black                                                       SBR-1712 +     --   --   --  137.50                                                                            --  --                                       5.0 parts of 60/40                                                            MA/Bd dispersant                                                              and carbon black                                                              SBR-1712 +     --   --   --  --  137.50                                                                            --                                       2.5 parts 50/50                                                               MA/Bd dispersant                                                              and carbon black                                                              SBR-1712 +     --   --   --  --  --  137.50                                   5.0 parts 50/50                                                               MA/Bd dispersant                                                              and carbon black                                                              ZnO            3.00 3.00 3.00                                                                              3.00                                                                              3.00                                                                              3.00                                     Stearic Acid   1.35 1.35 1.35                                                                              1.35                                                                              1.35                                                                              1.35                                     Sulfur         1.75 1.75 1.75                                                                              1.75                                                                              1.75                                                                              1.75                                     Accelerator    1.40 1.40 1.40                                                                              1.40                                                                              1.40                                                                              1.40                                     Rheometer, 300 F, 3 Deg.                                                      ARC, 100 CPM, 60 MIN.                                                         MOTOR                                                                         Torque, min.   12.7 14.2 14.2                                                                              11.0                                                                              13.6                                                                              17.9                                     Torque, max.   56.8 57.4 57.7                                                                              54.2                                                                              54.9                                                                              63.1                                     TS 2           12.0 12.7 12.6                                                                              13.8                                                                              12.2                                                                              10.8                                     T'C90          33.6 35.0 34.9                                                                              35.9                                                                              36.8                                                                              35.3                                     T'C95          41.0 42.0 42.0                                                                              43.0                                                                              43.7                                                                              43.9                                     ML-4 MIN./212F 59.  62.  64. 52. 62. 79.                                      GARVEY DIE EXTRUSION                                                          Inches/min.    19.  19.  19. 20. 19. 20.                                      Grams/min.     256. 278. 281.                                                                              263.                                                                              254.                                                                              300.                                     Grams/inch     13.48                                                                              14.78                                                                              14.56                                                                             13.26                                                                             13.41                                                                             14.75                                    AUTOGRAPHIC TENSILE                                                           Tensile, psi   2900.                                                                              3200.                                                                              3050.                                                                             2825.                                                                             3100.                                                                             3275.                                    Elongation, %  600. 620. 610.                                                                              620.                                                                              660.                                                                              570.                                     300% modulus   1150.                                                                              1250.                                                                              1175.                                                                             1150.                                                                             1100.                                                                             1400.                                    Hardness, Shore A                                                                            63.  65.  66. 68. 66. 66.                                      Best Cure, Min. at                                                                           40.  40.  40. 40. 40. 40.                                      300 F                                                                         Specific gravity                                                                             1.154                                                                              1.157                                                                              1.160                                                                             1.160                                                                             1.161                                                                             1.158                                    Tear, Die (c) ppi                                                                            270. 273. 271.                                                                              280.                                                                              262.                                                                              293.                                     Compression Set (b), %                                                                       14.3 16.4 17.8                                                                              20.5                                                                              14.7                                                                              12.3                                     22 hrs./158F                                                                  Pico abrasion  93.  101. 98. 102.                                                                              95. 100.                                     Index                                                                         Goodyear-Healey Rebound                                                       & Deflection                                                                  Cold rebound, %                                                                              49.6 49.1 47.7                                                                              45.9                                                                              45.0                                                                              49.6                                     Deflection, in.                                                                              .232 .225 .219                                                                              .215                                                                              .222                                                                              .222                                     Hot rebound, % 67.3 67.9 67.3                                                                              63.5                                                                              66.2                                                                              70.1                                     Deflection, in.                                                                              .284 .281 .278                                                                              .277                                                                              .286                                                                              .275                                     Dynamic Modulus, 212F                                                         E              62.3 67.8 66.5                                                                              68.9                                                                              63.9                                                                              70.6                                     N              27.7 31.7 31.2                                                                              37.4                                                                              31.7                                                                              29.1                                     R              34.0 32.6 31.9                                                                              27.0                                                                              30.0                                                                              36.6                                     H(X)           105.7                                                                              117.4                                                                              116.4                                                                             129.2                                                                             114.8                                                                             115.0                                    H(F)           121.9                                                                              114.3                                                                              117.7                                                                             121.9                                                                             126.2                                                                             103.4                                    Goodyear 66% Flex at                                                          Room Temperature                                                              Min. to fail   240. 240. 240.                                                                              240.                                                                              240.                                                                              240.                                     Min. to fail   240. 240. 240.                                                                              240.                                                                              240.                                                                              240.                                     Min. to fail   240. 240. 240.                                                                              240.                                                                              240.                                                                              240.                                     Min. to fail   180. 240. 240.                                                                              240.                                                                              240.                                                                              240.                                     Average        225.0                                                                              240.0                                                                              240.0                                                                             240.0                                                                             240.0                                                                             240.0                                    No. fail       3.   4.   4.  4.  4.  4.                                       Air Bomb Aging -                                                              16 Hrs./236F/80 psi                                                           Tensile, psi   2475.                                                                              2500.                                                                              2550.                                                                             2400.                                                                             2600.                                                                             2600.                                    % retained     85.  78.  84. 85. 84. 79.                                      Elongation, %  425. 420. 430.                                                                              425.                                                                              480.                                                                              420.                                     % retained     71.  68.  70. 69. 73. 74.                                      Hardness, Shore A                                                                            72.  73.  73. 76. 74. 74.                                      Point change   9.   8.   7.  8.  8.  8.                                       __________________________________________________________________________

INDUSTRIAL APPLICABILITY

The artisan will appreciate that the present invention satisfies a longfelt need in this technical area. Presently accepted methods forpreparing black dispersions result in low solids reinforcing dispersionswhich do not mix well with rubber latex. Heretofore, the use ofdispersing agents generally resulted in a decline in physical propertiesin the final rubber product. The present invention provides a method forpreparing high solids content reinforcing agent dispersion of excellentstability which mix easily with latices and do not diminish final rubberproduct properties.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the scope of the invention.

We claim:
 1. A process for blending rubber latex and a reinforcing agentby stirring and dispersing a mixture of the reinforcing agent selectedfrom the group consisting essentially of carbon black and precipitatedhydrated amorphous silicas in the rubber latex, the improvementcomprising initially contacting the reinforcing agent with a 60/40 to40/60 butadiene/methacrylic acid dispersing latex which has beenconverted to a water soluble form through treatment with an alkali metalhydroxide at a ratio of dry reinforcing agent to dispersing latex solidsin the range of from 90:10 to 99:1.
 2. A process according to claim 1wherein the dry reinforcing agent is carbon black.
 3. A processaccording to claim 1 wherein the dry reinforcing agent is carbon blackand the ratio of dry carbon black to dispersing latex solids is from95:5 to 98:2.
 4. A process according to claim 1 wherein the ratio ofbutadiene to methacrylic acid in the dispersing latex is 50/50.
 5. Aprocess for the preparation of reinforcing agent-pigment rubber latexmixture which comprises initially contacting the reinforcing agentselected from the group consisting essentially of carbon black andprecipitated hydrated amorphous silicas with a butadiene/methacrylicacid dispersing latex which has been converted to a water soluble formthrough treatment with an alkali metal hydroxide at a ratio of dryreinforcing agent-pigment to latex solids in the range of from 90:10 to99:1, thereafter adding the reinforcing agent-pigmentbutadiene/methacrylic acid mixture to a rubber latex to be reinforced inconventional amounts under conventional conditions.
 6. A processaccording to claim 5 wherein the dry reinforcing agent is carbon black.7. A process according to claim 5 wherein the dry reinforcing agent iscarbon black and the ratio of dry carbon black to dispersing latexsolids is from 95:5 to 98:2.
 8. A process according to claim 5 whereinthe butadiene/methacrylic acid dispersing latex has a ratio of 50/50,butadiene to methacrylic acid and the ratio of dry reinforcing agentpigment to latex solids ranges from 95:5 to 98:2.